1. Field of the Inventiion
The invention relates generally to printers and it has reference in particular to serial printers and a method of operation thereof wherein a single print element such as a rotating print wheel and an associated print hammer are moved along the print line of a document to print thereon.
2. Description of the Prior Art
Serial line printers are known in which the print mechanism comprises a single print element having plural type characters arranged in one or more sets in a predetermined sequence thereon. The print mechanism is operated to move or orient the print element to present the desired characters to be printed at a print position where contact is made with a record medium. A line of characters or other symbols is formed by effecting a lateral motion of the print mechanism and the record medium along a print line comprised of a plurality of uniformly-spaced print positions on a record medium. The operation of the print mechanism and its lateral movement must be coordinated so that the desired type is in position to make contact with the record medium when the print mechanism has moved to the desired print location. The rate at which single print element printers can print characters basically depends on the operation or set-up time required by the print mechanism; that is, the time for the print element to be moved to bring the next desired character into position to be actuated to make contact with the paper and recover for the next print operation.
Various ways have been devised to increase the throughput rate of serial printers. For example, in U.S. Pat. No. 3,461,225, issued on Aug. 12, 1967 to F. P. Willcox et al, entitled "Data Transmission System and Printer", a single print element comprises a disk or wheel with plural characters formed on flexible fingers around the periphery of the wheel. The typewheel and its hammer mechanism are mounted on a carrier which is moved laterally in a step-like motion along the print line. The typewheel is rotated at a constant speed at a rate such that a complete set of characters is presented for printing at each print position. In U.S. Pat. No. 3,371,766, issued Mar. 5, 1968 to Karel J. Staller, entitled "Printing Apparatus" and U.S. Pat. No. 3,356,199, issued Dec. 5, 1967 to Leland P. Robinson, entitled "Printer Having Type Disk Rotatable In A Plane Parallel To The Printing Line", the typewheel is rotated continuously while being transported continuously by the carrier along the print line. While the continuously moving carrier provides an increased throughput printing rate over the incremental carrier movement, the velocity of the carrier must coincide with the maximum time required for the typewheel to position a complete set of type characters at each print position.